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Unformatted text preview: Esha Roy Lab TA: Yunsheng Luo The Effect of Changing pH on Rate of Glucose Fermentation by Yeast Introduction All organisms require energy to carry out their cellular processes, which most obtain by undergoing cellular respiration to metabolize organic compounds and make ATP. Cellular respir- ation begins with glycolysis, or the conversion of glucose, a six carbon compound, into two or- ganic, 3 carbon molecules of pyruvate. Pyruvate is later converted to Acetyl CoA, a compound that is used in the Krebs cycle to make NADH and FADH2, which are electron carriers that transfer electrons to an electron transport chain that ultimately forms ATP. This process requires oxygen as an ultimate electron acceptor at the end of the electron transport chain, and without oxygen present, cellular respiration cannot occur past glycolysis, which does not require oxygen (Songer, 2006). Under anaerobic conditions, the procedure of fermentation is used as an alternat- ive to the oxidative phosphorylation used in cellular respiration. Fermentation utilizes the initial step of cellular respiration, glycolysis, to convert glucose to 2 pyruvate molecules, which reduces NAD+ into NADH and yields a small amount of ATP in the process (Bruinenberg, 2004). In alcoholic fermentation, the pyruvate is then converted to 2 molecules of acetaldehyde by the removal of two molecules of CO2, which is then converted to ethanol in the oxidation of the NADH produced in glycolysis into NAD+. Knowing that the two products of alcoholic fermentation are ethanol and CO2, one can determine if fermentation has occurred in a reaction by noting if any CO2 has been produced as it bubbles out of the solution (Sener, 2006). Among several other organisms, the Saccharomyces cerevisiae species of yeast is a fungus that undergoes alcoholic fermentation to break down carbohydrates. This yeast and its use of fermentation has been utilized for many years to produce bread when the starch in the flour is broken down into glucose and fructose, which is ultimately converted to ethanol as previ- ously mentioned (Maiorella, 1982). The rate of fermentation has been proven to be affected by many factors such as yeast concentration, glucose concentration, and temperature (Sener, 2006). In this experiment, we will measure how different conditions of pH affect the fermenta- tion rate of the Saccharomyces cerevisiae yeast acting upon glucose to produce CO2 and ethanol. Yeast may be subjected to varying levels of pH according to their environment when the are un- dergoing fermentation, and we wanted to test how the viability of fermentation changed accord- ing to the different environmental conditions of varying pH. We will introduce solutions of equal concentrations of glucose and yeast to buffers of pH 4, 7, and 10, as well as one without any pH buffer to use as a control. We will keep these four solutions at a constant 37 C temperature and then measure the amount of CO2 evolved in the flask every 2 minutes over a 20 minute time in-...
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